SANAA, Yemen — An explosion ripped through crowds of looters in a
munitions factory Monday, killing at least 78 and injuring scores in the
latest sign of weakening government authority amid Yemen’s
two-month-old populist uprising.

The accidental blast came after soldiers
abandoned the factory, allowing the looters to enter — one of a series
of incidents in recent days in which government forces have left their
posts. They include areas in the north, where rebels have long
challenged the state’s authority, and the south, where al-Qaeda’s Yemen
branch and secessionists have confronted government forces for years,
according to Yemeni and opposition officials, diplomats and local news
reports.

The spreading instability underscores growing concerns by the United States and its allies that this fragile but strategic Middle Eastern nation could collapse if its political tensions are not
peacefully resolved. It comes as high-level negotiations between
President Ali Abdullah Saleh and his opponents over a handover of power have stalled in recent days. Saleh declared that he would give no more concessions to the opposition.